In order to meet the science goals of the PLATO space mission, an extensive science calibration and validation plan has been designed. This paper describes this plan, as well as the methodology adopted to select the science calibration and validation stars that have entered its input catalogue. This is the so-called scvPIC, which is part of the general PLATO Input Catalogue (PIC) for the first selected long pointing field in the Southern Hemisphere known as LOPS2. While many of PLATO's science requirements needed dedicated stars as calibrators as discussed here, its most stringent requirement is the delivery of the age of the host stars of exoplanetary systems with an accuracy better than 10% for a G0V star of V = 10 mag, i.e. a nearby Sun-like star. This is presently not within reach for large populations of dwarfs and subgiants in the Milky Way as it requires the models of their stellar interiors to be improved. We discuss how this ambitious age requirement led to the selection of tens of thousands of red giants, and of thousands of main-sequence early F-type gravity-mode pulsators in order to deduce their internal rotation profile across stellar evolution. This asteroseismic observable will then be imported as key information into improved models of dwarfs and subgiants in the Milky Way as optimal modelling tools for ever better age-dating of the exoplanet hosts as the PLATO mission moves along. Additional calibrators and validators included in the scvPIC are a few thousands of binaries, a few hundreds of legacy and benchmark stars, a few hundred photometrically stable stars, and six transiting brown dwarfs.

Only 40 exoplanetary systems with five or more planets are currently known. These systems are crucial for our understanding of planet formation and planet-planet interaction. The M dwarf L 98-59 has previously been found to show evidence of five planets, three of which are transiting. Our aim is to confirm the fifth planet in this system and to refine the system characteristics namely minimum masses, radii and the orbital parameters of the planets around L 98-59. We reanalysed RV and activity data from HARPS and ESPRESSO alongside TESS and HST transit data using a joint model. The parameter space was sampled using the dynesty nested sampler. We confirm the previously known fifth planet in the system's habitable zone with an orbital period of 23.069(-0.082)(+0.081) days, a minimum mass of 2.97(-0.48)(+0.46)M(circle plus) and an equilibrium temperature of 284 K. We find an additional planet candidate in the RV data with an orbital period of 1.736 15(-0.000)(+0.000) (74)(76) days and a minimum mass of 0.58 +/- 0.12M(circle plus). This candidate (L 98-59.06) has a statistical significance between 2.9 sigma and 4.2 sigma, details depending on the modelling of stellar variability. Moreover, we present evidence for a stellar rotation period of 76.6(-4.2)(+4.1) days.

A few weeks after launch, the PLATO spacecraft is expected to start its payload commissioning, which will be completed within the first three months of the mission. This phase includes the in-orbit verification, calibration, and configuration of the instrument prior to nominal science operations. During this mission-critical period, and again later during regular spacecraft rotations and re-pointings, a set of reference stars is required to complete various calibration steps. This set, referred to as the calibration PLATO Input Catalog (cPIC), is part of the PIC. The cPIC comprises various stellar samples, each serving a dedicated technical calibration purpose, and it contains 71671 unique stellar targets across PLATO's entire field of view (FoV). Once the spacecraft commences science observations, the on-board Fine Guidance System (FGS) will rely on a small set of guide stars. These stars must be particularly bright and will be observed with the two fast cameras, which cover only a smaller central region of PLATO's FoV. This target list, referred to as the fine-guidance PLATO Input Catalog (fgPIC), contains 2640 unique targets, of which about 30 are used by the FGS at any given time. In this paper, we present the selection criteria for both the cPIC and the fgPIC, and asses their impact on the construction of these calibration catalogs for PLATO.

Simulated differential transmission spectra of various “superhabitable” planet scenarios. For comparison, the predicted spectra of Kepler-62e (a terrestrial planet in the habitable zone of a K dwarf) and the modern Earth around the Sun are shown as well. Spectral features are displayed in ppm relative to each planet's baseline transit depth, revealing individual molecular signatures, including O 2 , O 3 , CH 4 , H 2 O, N 2 O, CO 2 , CH 3 Cl, and CO. Solid gray lines represent planets receiving an incident stellar flux of 0.8 solar constants ( S 0 = 1366 W/m 2 ), positioned between the inner edge and center of their respective host star's habitable zone, while dashed lines represent the same planets at 0.6 S 0, aligned with the center of the habitable zone. The prospects of observing possible biosignatures in the atmospheres of transiting “superhabitable” exoplanets with the James Webb Space Telescope are discussed in the related paper by I. Vilović et al. published in this issue e20240081 .

The European Space Agency has selected PLATO (PLAnetary Transits and Oscillations of stars) for its M3 launch which is scheduled for 2026. With its extremely large field of view, PLATO is designed to obtain photometric measurements over an extended period for bright stars in order to detect and characterise (primarily) rocky planets in the habitable zones of solar type stars. The PLATO measurements will have sufficient sensitivity to determine the mass, radius and age of the host stars with unprecedented accuracy. The PLATO planet database will provide the first large-scale catalogue of accurately and homogeneously characterised small planets at intermediate orbital periods, which will can be used to severely constraint planet formation theories. This would facilitate large scale comparative exo-planetology. In addition the bright PLATO host stars will be ideal targets for atmospheric study with next generation facilities such as the ELT. The PLATO sensitivity will be sufficient to detect pulsations from stars across the HR diagram allowing a deep understanding of stellar structure and evolution to be developed using parameters determined from asteroseismology.

In our search for life beyond the Solar System, certain planetary bodies may be more conducive to life than Earth. However, the observability of these "superhabitable" (SH) planets in the habitable zones around K dwarf stars has not been fully modeled. This study addresses this gap by modeling the atmospheres of SH exoplanets. We employed the 1D model Atmos to define the SH parameter space, POSEIDON to calculate synthetic transmission spectra, and PandExo to simulate JWST observatisolar flux, are optimal for life. These planets sustain temperate surfaces with moderate CO2 levelons. Our results indicate that planets orbiting mid-type K dwarfs, receiving 80% of Earth's s, unlike those receiving 60% flux, where necessarily higher CO2 levels could hinder biosphere development. Moreover, they are easier to observe, requiring significantly fewer transits for biosignature detection compared with Earth-like planets around Sun-like stars. For instance, detecting biosignature pairs like oxygen and methane from 30 pc would require 150 transits (43 years) for a SH planet, versus over 1700 transits (similar to 1700 years) for Earth-like planets. While such observation times lie outside of JWST mission timescales, our study underscores the necessity of next-generation telescopes and provides valuable targets for future observations with, for example, the ELT.

With interstellar mission concepts now being under study by various space agencies and institutions, a feasible and worthy interstellar precursor mission concept will be key to the success of the long shot. Here we investigate interstellar-bound trajectories of solar sails made of the ultra-light material aerographite, known for its low density (0.18 kg m$^{-3}$) and high absorptivity ($\mathcal{A}{\sim}1$), enabling remarkable solar irradiation-based acceleration. Payloads of up to 1 kg can swiftly traverse the solar system and the regions beyond. Our simulations consider various launch scenarios from a polar orbit around the Earth with direct outbound trajectories and Sun diver launches with subsequent outward acceleration. Utilizing the poliastro Python library, we calculate positions, velocities, and accelerations for a 1 kg spacecraft (including 720 g aerographite mass) with 10$^4$ m$^2$ of cross-sectional area, corresponding to a 56 m radius. A direct outward Mars transfer yields 65 km s$^{-1}$ in 26 d. The inward Mars transfer, with a sail deployment at a minimum distance of 0.6 AU, achieves 118 km s$^{-1}$ in 126 d. Transfer times and velocities vary due to the Earth-Mars constellation and initial injection trajectory. The direct interstellar trajectory peaks at 109 km s$^{-1}$, reaching interstellar space in 5.3 yr defined by the heliopause at 120 AU. Alternatively, the initial Sun dive to 0.6 AU provides 148 km s$^{-1}$ of escape velocity, reaching the heliopause in 4.2 yr. Values differ based on the minimum distance to the Sun. Presented concepts enable swift Mars flybys and interstellar space exploration. For delivery missions of sub-kg payloads, the deceleration remains a challenge.

Transiting planets around young stars are hard to find due to the enhanced stellar activity. Only a few transiting planets have been detected around stars younger than 100 Myr. We initially detected a transit-like signal in the K2 light curve of a very cool M dwarf star (EPIC 211101996) in the Pleiades open cluster, with an estimated age of about 100 Myr. Our detailed analysis of the per-pixel light curves, detrending with the Wōtan software and transit search with the Transit Least Squares algorithm showed that the source of the signal is a contaminant source (Gaia DR3 66767847894609792) 20" west of the target. The V-like shape of its phase-folded light curve and eclipse depth of 15 hitherto been listed as a single star, which we now identify as an eclipsing stellar binary with a period of about 6 days.

The $ sim 23$\,Myr young star beta \,Pictoris (beta \,Pic) is a laboratory for planet formation studies because of its observed debris disk, its directly imaged super-Jovian planets beta \,Pic\,b and c, and the evidence of extrasolar comets that regularly transit in front of the star. The most recent evidence of exocometary transits around beta \,Pic came from stellar photometric time series obtained with the TESS space mission. Previous analyses of these transits constrained the orbital distribution of the underlying exocomet population to a range between about 0.03 and 1.3\,AU assuming a fixed transit impact parameter. We examine the distribution of the observed transit durations Delta t$) to infer the orbital surface density distribution (delta ) of the underlying exocomet sample. The effect of the geometric transit probability for circular orbits was properly taken into account, but we assumed that the radius of the transiting comets and their possible clouds of evaporating material are much smaller than the stellar radius. We show that a narrow belt of exocomets around beta \,Pic, in which the transit impact parameters are randomized but the orbital semimajor axes are equal, results in a pile-up of long transit durations. This is in contrast to observations, which reveal a pile-up of short transit durations Delta t 0.1$\,d) and a tail of only a few transits with Delta t > 0.4$\,d. A flat density distribution of exocomets between about 0.03 and 2.5\,AU results in a better match between the resulting Delta t$ distribution and the observations, but the slope of the predicted $ Delta t$ histogram is not sufficiently steep. An even better match to the observations can be produced with a $ beta $ power law. Our modeling reveals a best fit between the observed and predicted $ Delta t$ distribution for $ A more reasonable scenario in which the exocometary trajectories are modeled as hyperbolic orbits can also reproduce the observed $ Delta t$ distribution to some extent. Future studies might reproduce the observed $ Delta t$ distribution with a full exploration of the four-dimensional parameter space of highly eccentric orbits, and they might need to relax our assumption that the transiting objects are smaller than the stellar disk. The number of observed exocometary transits around beta \,Pic is currently too small to validate the previously reported distinction of two distinct exocomet families, but this might be possible with future TESS observations of this star. Our results nevertheless imply that cometary material exists on highly eccentric orbits with a more extended range of semimajor axes than suggested by previous spectroscopic observations.

The TEMPO (Transiting Exosatellites, Moons, and Planets in Orion) Survey is a proposed 30-day observational campaign using the Nancy Grace Roman Space Telescope. By providing deep, high-resolution, short-cadence infrared photometry of a dynamic star-forming region, TEMPO will investigate the demographics of exosatellites orbiting free-floating planets and brown dwarfs – a largely unexplored discovery space. Here, we present the simulated detection yields of three populations: extrasolar moon analogs orbiting free-floating planets, exosatellites orbiting brown dwarfs, and exoplanets orbiting young stars. Additionally, we outline a comprehensive range of anticipated scientific outcomes accompanying such a survey. These science drivers include: obtaining observational constraints to test prevailing theories of moon, planet, and star formation; directly detecting widely separated exoplanets orbiting young stars; investigating the variability of young stars and brown dwarfs; constraining the low-mass end of the stellar initial mass function; constructing the distribution of dust in the Orion Nebula and mapping evolution in the near-infrared extinction law; mapping emission features that trace the shocked gas in the region; constructing a dynamical map of Orion members using proper motions; and searching for extragalactic sources and transients via deep extragalactic observations reaching a limiting magnitude of m_AB=29.7 mag (F146 filter).

The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy was the construction of an observatory capable of characterizing habitable worlds. In this paper series we explore the detectability of and interference from exomoons and exorings serendipitously observed with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting in this manuscript with Earth–Moon analog mutual events. Unlike transits, which only occur in systems viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every star–planet–moon system. The cadence of these events can vary widely from ∼yearly to multiple events per day, as was the case in our younger Earth–Moon system. Leveraging previous space-based (EPOXI) light curves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive the detectability of Moon analogs with HWO. We determine that Earth–Moon analogs are detectable with observation of ∼2–20 mutual events for systems within 10 pc, and larger moons should remain detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet features and weather. We find that HWO wavelength coverage in the near-infrared, specifically in the 1.4 μ m water band where large moons can outshine their host planet, will aid in differentiating exomoon signals from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin to our Moon are more likely to be detected in younger systems, where shorter orbital periods and favorable geometry enhance the probability and frequency of mutual events.

Stars with about 45 to 80% the mass of the Sun, so-called K dwarf stars, have previously been proposed as optimal host stars in the search for habitable extrasolar worlds. These stars are abundant, have stable luminosities over billions of years longer than Sun-like stars, and offer favourable space environmental conditions. So far, the theoretical and experimental focus on exoplanet habitability has been on even less massive, though potentially less hospitable red dwarf stars. Here we present the first experimental data on the responses of photosynthetic organisms to a simulated K dwarf spectrum. We find that garden cress Lepidium sativum under K-dwarf radiation exhibits comparable growth and photosynthetic efficiency as under Solar illumination on Earth. The cyanobacterium Chroococcidiopsis sp. CCMEE 029 exhibits significantly higher photosynthetic efficiency and culture growth under K dwarf radiation compared to Solar conditions. Our findings of the affirmative responses of these two photosynthetic organisms to K dwarf radiation suggest that exoplanets in the habitable zones around such stars deserve high priority in the search for extrasolar life.

In our search for life in the Universe, there may be planetary bodies that are more conducive to life than Earth. Even Earth's habitability has varied enormously throughout the eons. We call worlds that are more habitable than Earth today ‘superhabitable’. In the pursuit of superhabitable worlds, K dwarf stars emerge as promising candidates due to their stable luminosity evolution, offering prolonged stability within the habitable zone conducive to life's emergence and sustainability (Arney 2019; Heller and Armstrong 2014; Schulze-Makuch, Heller, and Guinan 2020). A planet with up to 2 times Earth’s mass and around 25% larger than Earth orbiting such a K dwarf star could qualify as superhabitable. Such dimensions would result in surface pressures of roughly 1.2 bar, exceeding Earth's current pressure by 20%. This configuration would offer expanded living space and enable the retention of a denser atmosphere, providing the necessary mass and energy to support a more extensive biosphere. Moreover, the denser atmosphere would enhance detectability through remote observations. A superhabitable planet would also likely exhibit a slightly warmer climate than present-day Earth, with temperatures elevated by approximately 5 degrees Celsius. This modest increase aligns with historical trends, as biodiversity flourished during warmer epochs, with tropical zones hosting the majority of Earth's current biodiversity (Vilović, Schulze-Makuch, and Heller 2023). In terms of atmospheric compositions, such planets would exhibit heightened oxygen concentrations which contribute to expanded metabolic networks and support larger body sizes among organisms. In our most recent study, we tested the effects of simulated K-dwarf radiation on the phototrophic organisms garden cress and cyanobacteria using an LED stellar simulator. We found that both organisms are capable of growing under this modified radiation environment, with cyanobacteria exhibiting significantly better responses to K dwarf compared to solar radiation (Vilović et al. 2024). Expanding upon these laboratory results, we now turn to theoretical models to assess the detectability of superhabitability with the James Webb Space Telescope (JWST). We combine the results of the 1D coupled climate-photochemistry model Atmos for modeling superhabitable atmospheres (Kopparapu et al. 2013) as well as the POSEIDON forward modeling code to calculate synthetic planetary spectra (MacDonald and Madhusudhan 2017; MacDonald 2023), with the PandExo tool for simulating observations of transiting exoplanets with the JWST (Batalha et al. 2017). Preliminary results indicate that superhabitable conditions positively impact the observability of key spectral features, including the oxygen features at 0.69, 0.77 and 1.24 micrometers, as well as the carbon dioxide feature at 4.3 micrometers and the ozone feature at 9.6 micrometers. Furthermore, these spectral features may require fewer transits for detection with the JWST compared to a modern Earth counterpart. This underscores the importance of prioritizing exoplanets orbiting K dwarf stars within the center of their habitable zones in our search for life outside of the Solar System using state of the art instrumentation. ReferencesArney, Giada N. 2019. “The K Dwarf Advantage for Biosignatures on Directly Imaged Exoplanets.” The Astrophysical Journal Letters 873 (1): L7.Batalha, Natasha E., Avi Mandell, Klaus Pontoppidan, Kevin B. Stevenson, Nikole K. Lewis, Jason Kalirai, Thomas Greene, Loïc Albert, Louise D. Nielsen, and Nick Earl. 2017. “PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST.” arXiv [astro-ph.IM]. arXiv. http://arxiv.org/abs/1702.01820.Heller, René, and John Armstrong. 2014. “Superhabitable Worlds.” Astrobiology. https://doi.org/10.1089/ast.2013.1088.Kopparapu, Ravi Kumar, Ramses Ramirez, James F. Kasting, Vincent Eymet, Tyler D. Robinson, Suvrath Mahadevan, Ryan C. Terrien, Shawn Domagal-Goldman, Victoria Meadows, and Rohit Deshpande. 2013. “Habitable Zones around Main-Sequence Stars: New Estimates.” The Astrophysical Journal 765 (2): 131.MacDonald, Ryan J. 2023. “POSEIDON: A Multidimensional Atmospheric Retrieval Code for Exoplanet Spectra.” Journal of Open Source Software 8 (81): 4873.MacDonald, Ryan J., and Nikku Madhusudhan. 2017. “HD 209458b in New Light: Evidence of Nitrogen Chemistry, Patchy Clouds and Sub-Solar Water.” Monthly Notices of the Royal Astronomical Society 469 (August): 1979–96.Schulze-Makuch, Dirk, René Heller, and Edward Guinan. 2020. “In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World.” Astrobiology 20 (12): 1394–1404.Vilović, Iva, Dirk Schulze-Makuch, and René Heller. 2023. “Variations in Climate Habitability Parameters and Their Effect on Earth’s Biosphere during the Phanerozoic Eon.” Scientific Reports 13 (1): 12663.Vilović, I., Schulze-Makuch, D. & Heller, R. (2024). Observation of Significant Photosynthesis in Garden Cress and Cyanobacteria under Simulated Illumination from a K Dwarf Star. International Journal of Astrobiology. (In Review)

There are more than 200 moons in our Solar System, but their relatively small radii make similarly sized extrasolar moons very hard to detect with current instruments. The best exomoon candidates so far are two nearly Neptune-sized bodies orbiting the Jupiter-sized transiting exoplanets Kepler-1625 b and Kepler-1708 b, but their existence has been contested. Here we reanalyse the Hubble and Kepler data used to identify the two exomoon candidates employing nested sampling and Bayesian inference techniques coupled with a fully automated photodynamical transit model. We find that the evidence for the Kepler-1625 b exomoon candidate comes almost entirely from the shallowness of one transit observed with Hubble. We interpret this as a fitting artefact in which a moon transit is used to compensate for the unconstrained stellar limb darkening. We also find much lower statistical evidence for the exomoon candidate around Kepler-1708 b than previously reported. We suggest that visual evidence of the claimed exomoon transits is corrupted by stellar activity in the Kepler light curve. Our injection-retrieval experiments of simulated transits in the original Kepler data reveal false positive rates of 10.9% and 1.6% for Kepler-1625 b and Kepler-1708 b, respectively. Moreover, genuine transit signals of large exomoons would tend to exhibit much higher Bayesian evidence than these two claims. We conclude that neither Kepler-1625 b nor Kepler-1708 b are likely to be orbited by a large exomoon. A reanalysis of Kepler and Hubble data with Bayesian inference and a photodynamical model shows that the two exomoon candidates around Kepler-1625 b and Kepler-1708 b have a substantially lower probability to be actual detections than previous analyses suggest.

We present design considerations for the Transiting Exosatellites, Moons, and Planets in Orion (TEMPO) Survey with the Nancy Grace Roman Space Telescope. This proposed 30-day survey is designed to detect a population of transiting extrasolar satellites, moons, and planets in the Orion Nebula Cluster (ONC). The young (1-3 Myr), densely-populated ONC harbors about a thousand bright brown dwarfs (BDs) and free-floating planetary-mass objects (FFPs). TEMPO offers sufficient photometric precision to monitor FFPs with ${\rm M}\geq1{\rm M}_{\rm J}$ for transiting satellites. The survey is also capable of detecting FFPs down to sub-Saturn masses via direct imaging, although follow-up confirmation will be challenging. TEMPO yield estimates include 14 (3-22) exomoons/satellites transiting FFPs and 54 (8-100) satellites transiting BDs. Of this population, approximately $50\%$ of companions would be "super-Titans" (Titan to Earth mass). Yield estimates also include approximately $150$ exoplanets transiting young Orion stars, of which $>50\%$ will orbit mid-to-late M dwarfs and approximately ten will be proto-habitable zone, terrestrial ($0.1{\rm M}_{\oplus} - 5{\rm M}_{\oplus}$) exoplanets. TEMPO would provide the first census demographics of small exosatellites orbiting FFPs and BDs, while simultaneously offering insights into exoplanet evolution at the earliest stages. This detected exosatellite population is likely to be markedly different from the current census of exoplanets with similar masses (e.g., Earth-mass exosatellites that still possess H/He envelopes). Although our yield estimates are highly uncertain, as there are no known exoplanets or exomoons analogous to these satellites, the TEMPO survey would test the prevailing theories of exosatellite formation and evolution, which limit the certainty surrounding detection yields.

Essential insights on the characterization and quality of a detectable biosphere are gained by analyzing the effects of its environmental parameters. We compiled environmental and biological properties of the Phanerozoic Eon from various published data sets and conducted a correlation analysis to assess variations in parameters relevant to the habitability of Earth’s biosphere. We showed that environmental parameters such as oxygen, global average surface temperatures, runoff rates and carbon dioxide are interrelated and play a key role in the changes of biomass and biodiversity. We showed that there were several periods with a highly thriving biosphere, with one even surpassing present day biodiversity and biomass. Those periods were characterized by increased oxygen levels and global runoff rates, as well as moderate global average surface temperatures, as long as no large or rapid positive and/or negative temperature excursions occurred. High oxygen contents are diagnostic of biomass production by continental plant life. We find that exceptionally high oxygen levels can at least in one instance compensate for decreased relative humidities, providing an even more habitable environment compared to today. Beyond Earth, these results will help us to understand how environmental parameters affect biospheres on extrasolar planets and guide us in our search for extraterrestrial life.

In this White Paper for Nancy Grace Roman Space Telescope (Roman) science, we propose the Roman Survey of the Earth Transit Zone (RoSETZ), a transit search for rocky planets within the habitable zones (HZs) of stars located within the Earth Transit Zone (ETZ). The ETZ holds special interest in the search for extra-terrestrial intelligence (SETI) - observers on planets within the ETZ can see Earth as a transiting planet. RoSETZ would augment the Roman Galactic Bulge Time Domain Survey (GBTDS) as an additional field located $\sim 5$~degrees away from other GBTDS fields. Our simulations show that RoSETZ alone can find from 120 to 630 Earth-sized HZ planets around K- and M-type hosts, with the range reflecting different survey design assumptions. These yields are 5-20 times the number currently known. Such a sample will transform our knowledge of ``Eta-Earth'' ($\eta_{\oplus}$) -- the occurrence of Earth-sized HZ planets -- and would be the first catalogue of exoplanets selected in a manner optimized according to the Mutual Detectability targetted-SETI strategy. If it can be accommodated alongside the existing GBTDS design, we favour a RoSETZ-Max design that is observed for the duration of the GBTDS. If not, we show that a slimmed-down RoSETZ-Lite design, occupying two GBTDS seasons, would not significantly impact overall GBTDS exoplanet yields, even if time allocated to it had to come from time allocations to other fields. We argue that the angular separation of RoSETZ from other GBTDS fields permits self-calibration of systematic uncertainties that would otherwise hamper exoplanet demographic modelling of both microlensing and transit datasets. Other science possible with RoSETZ data include studies of small solar system bodies and high resolution 3D extinction mapping.

The K-type star TOI-2525 has an estimated mass of M = 0.849(-0.033)(+0.024) M-circle dot and radius of R = 0.785(-0.007)(+0.007) R-circle dot observed by the TESS mission in 22 sectors (within sectors 1 and 39). The TESS light curves yield significant transit events of two companions, which show strong transit timing variations (TTVs) with a semiamplitude of similar to 6 hr. We performed TTV dynamical and photodynamical light-curve analysis of the TESS data combined with radial velocity measurements from FEROS and PFS, and we confirmed the planetary nature of these companions. The TOI-2525 system consists of a transiting pair of planets comparable to Neptune and Jupiter with estimated dynamical masses of m(b) = 0.088(-0.004)(+0.005) and m(c) = 0.709(-0.033)(+0.034) M-Jup, radii of r(b) = 0.88(-0.02)(+0.02) and r(c) = 0.98(-0.02)(+0.02) R-Jup, and orbital periods of P-b = 23.288(-0.002)(+0.001) and P-c = 49.260(-0.001)(+0.001) days for the inner and outer planet, respectively. The period ratio is close to the 2:1 period commensurability, but the dynamical simulations of the system suggest that it is outside the mean-motion resonance (MMR) dynamical configuration. Object TOI-2525 b is among the lowest-density Neptune-mass planets known to date, with an estimated median density of rho(b) = 0.174(-0.015)(+0.016) g cm(-3). The TOI-2525 system is very similar to the other K dwarf systems discovered by TESS, TOI-2202 and TOI-216, which are composed of almost identical K dwarf primaries and two warm giant planets near the 2:1 MMR.

In the search for moons around extrasolar planets (exomoons), astronomers are confronted with a stunning observation. Although 3400 of the 4500 exoplanets were discovered with the transit method and although there are well over 25 times as many moons than planets known in the Solar System (two of which are larger than Mercury), no exomoon has been discovered to date. In the search for exoplanet transits, stellar light curves are usually phase-folded over a range of trial epochs and periods. This approach, however, is not applicable in a straightforward manner to exomoons. Planet-moon transits either have to be modeled in great detail (including their orbital dynamics, mutual eclipses, etc.), which is computationally expensive, or key simplifications have to be assumed in the modeling. One such simplification is to search for moon transits outside of the planetary transits. The question we address in this report is how much in-transit data of an exomoon remains uncontaminated by the near-simultaneous transits of its host planet. We develop an analytical framework based on the probability density of the sky-projected apparent position of an exomoon relative to its planet and test our results with a numerical planet-moon transit simulator. For exomoons with planet-moon orbital separations similar to the Galilean moons, we find that only a small fraction of their in-transit data is uncontaminated by planetary transits: 14 % for Io, 20 % for Europa, 42 % for Ganymede, and 73 % for Callisto. The signal-to-noise ratio (S/N) of an out-of-planetary-transit folding technique is reduced compared to a full photodynamical model to about 38 % (Io), 45 % (Europa), 65 % (Ganymede), and 85 % (Callisto), respectively. For the Earth’s Moon, we find an uncontaminated data fraction of typically just 18 % and a resulting S/N reduction to 42 %. These values are astonishingly small and suggest that the gain in speed for any exomoon transit search algorithm that ignores the planetary in-transit data comes at the heavy price of losing a substantial fraction of what is supposedly a tiny signal in the first place. We conclude that photodynamical modeling of the entire light curve has substantial, and possibly essential, advantages over folding techniques of exomoon transits outside the planetary transits, in particular for small exomoons comparable to those of the Solar System.

In its long-duration observation phase, the PLATO satellite will observe two non-overlapping fields for a total of 4 yr. The exact duration of each pointing will be determined 2 yr before launch. Previous estimates of PLATO's yield of Earth-sized planets in the habitable zones (HZs) around solar-type stars ranged between 6 and 280. We use the PLATO Solar-like Light curve Simulator (PSLS) to simulate light curves with transiting planets around bright (m_V > 11) Sun-like stars at a cadence of 25 s, roughly representative of the >15,000 targets in PLATO's high-priority P1 sample (mostly F5-K7 dwarfs and sub-dwarfs). Our study includes light curves generated from synchronous observations of 6, 12, 18, and 24 of PLATO's 12 cm aperture cameras over both 2 yr and 3 yr of continuous observations. Automated detrending is done with the Wotan software and post-detrending transit detection is performed with the Transit Least Squares (TLS) algorithm. We scale the true positive rates (TPRs) with the expected number of stars in the P1 sample and with modern estimates of the exoplanet occurrence rates and predict the detection of planets with 0.5 R_E <= R_p <= 1.5 R_E in the HZs around F5-K7 dwarf stars. For the (2 yr + 2 yr) long-duration observation phase strategy we predict 11-34 detections, for the (3 yr + 1 yr) strategy we predict 8-25 discoveries. Our study of the effects of stellar variability on shallow transits of Earth-like planets illustrates that our estimates of PLATO's planet yield, which we derive using a photometrically quiet star like the Sun, must be seen as upper limits. In conclusion, PLATO's detection of about a dozen Earth-sized planets in the HZs around solar-type stars will mean a major contribution to this yet poorly sampled part of the exoplanet parameter space with Earth-like planets.